The present invention relates to a heat treatment technique used in the field of semiconductor devices and particularly to a heat treatment method and a heat treatment apparatus for controlling the temperature of a substrate surface.
In recent years, as high integration of semiconductor devices has progressed, patterns have been miniaturized and preciseness thereof has been improved. In steps of manufacturing a photomask used for pattern exposure, a means for subjecting a photosensitive material to a heat treatment is necessary for the step of forming a pattern. In the process including the step of heating or cooling substrates to be exposed, variants of the treatment temperature are reflected on variants of the pattern size. Therefore, more precise management of the temperature has been demanded in accordance with miniaturization and improvement of the preciseness.
Conventionally, a thermocouple or a resistance bulb is embedded near the surface of a heating plate used for a heating treatment to measure the temperature, when managing the temperature of a substrate. Further, the output of a heating mechanism is controlled based on the obtained temperature, and a heat treatment is performed. However, since quartz forming the under layer of the substrate to be exposed has a very low thermal diffusivity, temperature of the photosensitive material film on the surface of the substrate to be processed cannot be accurately controlled by the method described above.
To perform precise temperature control with user of a quartz substrate used for a substrate to be exposed, it is necessary to measure directly the temperature of the film as a target to be subjected to a heat treatment on the substrate. Means for measuring the surface temperature are roughly divided into two types, one being a contact type and the other being a non-contact type, depending on the characteristics of a monitoring method.
As the contact type, there is a method of measuring the surface temperature by embedding a thermocouple into a film as a target on the substrate. However, it is not a realistic way to embed thermocouples into all substrates to be processed. Also, a photomask manufactured and processed by embedding directly a thermocouple in the substrate to be processed is not suitable for practical use. By attaching a thermocouple or a resistance member, the temperature characteristic is changed. Therefore, there is a problem that the photosensitive material film as a target to be heated cannot be accurately measured. In particular, it is impossible to embed a temperature sensor into a photosensitive material film having a film thickness of about 0.1 to 2 .mu.m called a resist.
From the reasons described above, it is preferable to use the temperature measuring method of the non-contact type. A radiation thermometer is a representative example of the temperature measuring device of this type. There is an example using the radiation thermometer which has succeeded in measurement of a surface temperature of a steel material having a precise oxide film processed by a shape steel line or the like.
However, the temperature measurement of a substrate to be processed or the like with use of the radiation thermometer involves the following problems. In this measurement, since the temperature of the temperature measurement area is as low as about 50 to 200.degree. C., the signal is weak. Therefore, if other radiated light than that from the target to be measured enters into the sensor section, a measurement error is caused. In addition, it is not possible to neglect a measurement error due to drifting of the sensitivity which is considered as depending on the environmental temperature and the like. From the reasons described above, the radiation thermometer involves a problem that accurate temperature measurement is difficult.
In addition, to obtain more precise patterns, it is highly necessary to use a step of measuring the temperature of the substrate surface with high preciseness and of performing heating (or cooling) based on the measurement result. Therefore, demands for a method and an apparatus, by which temperature measurement is carried out while monitoring the surface temperature of a substrate (in-situ) and feedback is immediately reflected on a heat control section or the like, have become more and more serious.